Ice Knocks Sensor Off Its Game

A customer called to comment on a dehumidification unit located in an ice arena.

“The unit uses so much energy we had to turn it off,” the customer said.

I asked about the percentage of relative humidity (RH) in the space. The customer indicated the controller showed high RH and the unit was running at 100 percent 24/7. The unit would not shut off, and the humidity did not change. When I asked the customer where the sensor was located, he said it was mounted on the wall about 10 ft off the ground.

Next, I asked him to verify the signal from the sensor to the controller. Sure enough, it was calling for full reactivation. I asked the customer to try and get several RH readings around the ice arena. When the customer called back, I realized his RH readings were well below the RH set point of the programmable logic controller (PLC). I then sent him a new sensor under warranty.

A week later, the customer called again. He had changed out the sensor, but there had been no change. I checked the factory test form, which showed the PLC and sensor had worked fine during tests. Therefore, either the PLC or the program must have an issue. Rather than send out more parts, we decided I would travel to the site to install a new PLC and program myself.

Upon arrival at the arena, I checked the sensor. Although it was mounted at a good height, it was located directly over a doorless room housing the Zamboni machine. When the Zamboni finishes clearing the ice, it backs into the room and dumps the ice shavings into a heated pit, which melts the ice.

I took 16 RH readings all over the arena and found that the area near the Zamboni room was way above set point, while the rest of the arena was well below set point. We moved the sensor to a more desirable location, and the unit started running correctly. I received a call from the customer a month later thanking me for fixing the issue and saving the arena a lot of money in energy costs.